Emerging role of topotecan in front-line treatment of carcinoma of the ovary

Demystifying the potential of inhibitors targeting DNA topoisomerases in unicellular protozoan parasites

DNA topoisomerases are a group of enzymes omnipresent in all organisms. They maintain the DNA topology during replication, repair, recombination, and transcription. However, the structure of topoisomerase in protozoan parasites differs significantly from that of human topoisomerases; thus, this enzyme acts as a crucial target in drug development against parasitic diseases. Although the therapeutic potential of drugs targeting the parasitic topoisomerase is well known, to manage the shortcomings of currently available therapeutics and the emergence of drug resistance, the discovery of novel antiparasitic molecules is an urgent need. In this review, we describe various investigational and repurposed topoisomerase inhibitors developed against protozoan parasites over the past few years. Teaser: Fatal parasitic diseases are an increasing cause for concern; here, we provide a compilation of different inhibitors targeting DNA topoisomerases, enzymes that are essential for, and unique to, protozoan parasites; therefore, inhibitors are efficient and have few adverse effects.

Characterization of a conjugated polysuccinimide-carboplatin compound

Carboplatin, an advanced anticancer drug with excellent efficacy against ovarian cancer, was developed to alleviate the side effects that often occur with cisplatin and other platinum-based compounds. Our study reports the in vitro characteristics, viability, and activity of cells expressing the inducible nitric oxide synthase (iNOS) gene after carboplatin was conjugated with polysuccinimide (PSI) and administered in combination with other widely used anticancer drugs. PSI, which has promising properties as a drug delivery material, could provide a platform for prolonging carboplatin release, regulating its dosage, and improving its side effects. The iNOS gene has been shown to play an important role in both cancer cell survival and inhibition. Herein, we synthesized a PSI-carboplatin conjugate to create a modified anticancer agent and confirmed its successful conjugation. To ensure its solubility in water, we further modified the structure of the PSI-carboplatin conjugate with 2-aminoethanol groups. To validate its biological characteristics, the ovarian cancer cell line SKOV-3 and normal ovarian Chinese hamster ovary cells were treated with the PSI-carboplatin conjugate alone and in combination with paclitaxel and topotecan, both of which are used in conventional chemotherapy. Notably, PSI-carboplatin conjugation can be used to predict changes in the genes involved in cancer growth and inhibition. In conclusion, combination treatment with the newly synthesized polymer-carboplatin conjugate and paclitaxel displayed anticancer activity against ovarian cancer cells but was not toxic to normal ovarian cancer cells, resulting in the development of an effective candidate anticancer drug without severe side effects.

Genome-wide identification and analysis of AP2/ERF transcription factors related to camptothecin biosynthesis in Camptotheca acuminata

Camptotheca acuminata produces camptothecin (CPT), a monoterpene indole alkaloid (MIA) that is widely used in the treatment of lung, colorectal, cervical, and ovarian cancers. Its biosynthesis pathway has attracted significant attention, but the regulation of CPT biosynthesis by the APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors (TFs) remains unclear. In this study, a systematic analysis of the AP2/ERF TFs family in C. acuminata was performed, including phylogeny, gene structure, conserved motifs, and gene expression profiles in different tissues and organs (immature bark, cotyledons, young flower, immature fruit, mature fruit, mature leaf, roots, upper stem, and lower stem) of C. acuminata. A total of 198 AP2/ERF genes were identified and divided into five relatively conserved subfamilies, including AP2 (26 genes), DREB (61 genes), ERF (92 genes), RAV (18 genes), and Soloist (one gene). The combination of gene expression patterns in different C. acuminata tissues and organs, the phylogenetic tree, the co-expression analysis with biosynthetic genes, and the analysis of promoter sequences of key enzymes genes involved in CPT biosynthesis pathways revealed that eight AP2/ERF TFs in C. acuminata might be involved in CPT synthesis regulation, which exhibit relatively high expression levels in the upper stem or immature bark. Among these, four genes (CacAP2/ERF123, CacAP2/ERF125, CacAP2/ERF126, and CacAP2/ERF127) belong to the ERF-B2 subgroup; two genes (CacAP2/ERF149 and CacAP2/ERF152) belong to the ERF-B3 subgroup; and two more genes (CacAP2/ERF095 and CacAP2/ERF096) belong to the DREB-A6 subgroup. These results provide a foundation for future functional characterization of the AP2/ERF genes to enhance the biosynthesis of CPT compounds of C. acuminata.

Externally Triggered Novel Rapid-Release Sonosensitive Folate-Modified Liposomes for Gemcitabine: Development and Characteristics

PURPOSE

To develop an externally triggered rapid-release targeted system for treating ovarian cancer, gemcitabine (GMC) was entrapped into sonosensitive (SoS) folate (Fo)-modified liposomes (LPs).

METHODS

GMC-loaded LPs (GMC LPs), GMC-loaded Fo-targeted LPs (GMC-Fo LPs), and GMC-loaded Fo-targeted SoS LPs (GMC-SoS Fo LPs) were prepared utilizing a film-hydration technique and evaluated based on particle size, ζ-potential, and percentage entrapped drug. Cellular uptake of the fluorescent delivery systems in Fo-expressing ovarian cancer cells was quantified using flow cytometry. Finally, tumor-targeting ability, in vivo evaluation, and pharmacokinetic studies were performed.

RESULTS

GMC LPs, GMC-Fo LPs, and GMC-SoS Fo LPs were successfully prepared, with sizes of <120.3±2.4 nm, 39.7 mV ζ-potential, and 86.3%±1.84% entrapped drug. Cellular uptake of GMC-SoS Fo LPs improved 6.51-fold over GMC LPs (under ultrasonic irradiation - p<0.05). However, cellular uptake of GMC-Fo LPs improved just 1.24-fold over GMC LPs (p>0.05). Biodistribution study showed that of GMC concentration in tumors treated with GMC-SoS-Fo LPs (with ultrasound) improved 2.89-fold that of free GMC (p<0.05). In vivo, GMC-SoS Fo LPs showed the highest antiproliferative and antitumor action on ovarian cancer.

CONCLUSION

These findings showed that externally triggered rapid-release SoS Fo-modified LPs are a promising system for delivering rapid-release drugs into tumors.

Chemotherapeutic resistance: a nano-mechanical point of view

Chemotherapeutic resistance is one of the main obstacles for cancer remission. To understand how cancer cells acquire chemotherapeutic resistance, biochemical studies focusing on drug target alteration, altered cell proliferation, and reduced susceptibility to apoptosis were performed. Advances in nano-mechanobiology showed that the enhanced mechanical deformability of cancer cells accompanied by cytoskeletal alteration is a decisive factor for cancer development. Furthermore, atomic force microscopy (AFM)–based nano-mechanical studies showed that chemotherapeutic treatments reinforced the mechanical stiffness of drug-sensitive cancer cells. However, drug-resistant cancer cells did not show such mechanical responses following chemotherapeutic treatments. Interestingly, drug-resistant cancer cells are mechanically heterogeneous, with a subpopulation of resistant cells showing higher stiffness than their drug-sensitive counterparts. The signaling pathways involving Rho, vinculin, and myosin II were found to be responsible for these mechanical alterations in drug-resistant cancer cells. In the present review, we highlight the mechanical aspects of chemotherapeutic resistance, and suggest how mechanical studies can contribute to unravelling the multifaceted nature of chemotherapeutic resistance.

Function of AP2/ERF Transcription Factors Involved in the Regulation of Specialized Metabolism in Ophiorrhiza pumila Revealed by Transcriptomics and Metabolomics

The hairy roots (HR) of Ophiorrhiza pumila produce camptothecin (CPT), a monoterpenoid indole alkaloid used as a precursor in the synthesis of chemotherapeutic drugs. O. pumila HR culture is considered as a promising alternative source of CPT, however, the knowledge about the biosynthetic pathway and regulatory mechanism is still limited. In this study, five genes that encode AP2/ERF transcription factors, namely OpERF1-OpERF5, were isolated from HR of O. pumila. Phylogenetic analysis of AP2/ERF protein sequences suggested the close evolutionary relationship of OpERF1 with stress-responsive ERF factors in Arabidopsis and of OpERF2 with ERF factors reported to regulate alkaloid production, such as ORCA3 in Catharanthus roseus, NIC2 locus ERF in tobacco, and JRE4 in tomato. We generated the transgenic HR lines of O. pumila, ERF1i and ERF2i, in which the expression of OpERF1 and OpERF2, respectively, was suppressed using RNA interference technique. The transcriptome and metabolome of these suppressed HR were analyzed for functional characterization of OpERF1 and OpERF2. Although significant changes were not observed in the metabolome, including CPT and related compounds, the suppression of OpERF2 resulted in reduced expression of genes in the 2-C-methyl-d-erythritol 4-phosphate and secologanin-strictosidine pathways, which supply a precursor, strictosidine, for CPT biosynthesis. Furthermore, while it was not conclusive for OpERF1, enrichment analysis of differentially expressed genes in the suppressed HR showed that the gene ontology terms for oxidation-reduction, presumably involved in secondary metabolite pathways, were enriched in the ERF2i downregulated gene set. These results suggest a positive role of OpERF2 in regulating specialized metabolism in O. pumila.

Topotecan plus carboplatin and paclitaxel in first-line treatment of advanced ovarian cancer: a meta-analysis of randomized controlled trials

OBJECTIVE

To evaluate whether the addition of topotecan can improve the efficacy of carboplatin and paclitaxel in first-line treatment of advanced epithelial ovarian cancer.

METHODS

Meta-analysis was performed using a random effects model.

RESULTS

Four randomized controlled trials with a total of 3632 patients were identified and included in the meta-analysis. No significant differences were observed in terms of progression-free survival (P=0.400), overall survival (P=0.502) and overall response rate (P=0.953) between patients treated with topotecan plus carboplatin and paclitaxel versus carboplatin and paclitaxel. However, there were significantly higher rates of grade 3-4 leucopenia (P=0.024), neutropenia (P<0.001), anaemia (P<0.001), and thrombopenia (P<0.001) in the topotecan plus carboplatin and paclitaxel group. No significant differences were observed in grade 3-4 nausea (P=0.352) and vomiting (P=0.092) between these two groups.

CONCLUSION

Topotecan plus carboplatin and paclitaxel did not improve survival outcomes and caused more haematological toxicity for advanced ovarian cancer.

Paclitaxel, topotecan, and carboplatin in metastatic endometrial cancinoma: a Hellenic Co-operative Oncology Group (HeCOG) study

OBJECTIVE

Taxanes, and platinum compounds represent the chemotherapeutic agents with the greatest activity in metastatic endometrial carcinoma. We administered the combination of paclitaxel, topotecan and carboplatin to patients with metastatic or recurrent carcinoma of the endometrium to evaluate its activity and to define its toxicity.

METHODS

Thirty-nine consecutive patients were treated on an outpatient basis with paclitaxel 150 mg/m(2), administered intravenously over a 3-h period and followed by carboplatin at AUC of 5 on day 3, with both agents proceding topotecan that was given at 0.75 mg/m(2)/day on days 1 through 3. The chemotherapy was repeated every 3 weeks with granulocyte colony-stimulating factor (G-CSF) support for a maximum of six courses.

RESULTS

Twenty-one (60%) patients achieved objective clinical response (95% CI, 42.2-75.7%) including 4 (11.4%) complete and 17 (48.6%) partial responses. The median times to progression and survival for all patients were 8.9 and 17.7 months, respectively. Grade 3 or 4 thombocytopenia and neutropenia occurred in 5 (13%) and 4 (10%) patients, respectively, but only 2 episodes of neutropenic fever were encountered. Grade 2 or 3 neurotoxicity was observed in 23% of patients.

CONCLUSIONS

The combination of paclitaxel, topotecan and carboplatin with G-CSF support appears active with acceptable toxicity in patients with metastatic or recurrent carcinoma of the endometrium.

A prospective randomized controlled trial of tumour chemosensitivity assay directed chemotherapy versus physician's choice in patients with recurrent platinum-resistant ovarian cancer

The primary aim of this randomized trial was to determine response rate and progression-free survival following chemotherapy in patients with platinum-resistant recurrent ovarian cancer, who had been treated according to an ATP-based tumour chemosensitivity assay in comparison with physician's choice. A total of 180 patients were randomized to assay-directed therapy (n=94) or physician's-choice chemotherapy (n=86). Median follow-up at analysis was 18 months. Response was assessable in 147 patients: 31.5% achieved a partial or complete response in the physician's-choice group compared with 40.5% in the assay-directed group (26 versus 31% by intention-to-treat analysis respectively). Intention-to-treat analysis showed a median progression-free survival of 93 days in the physician's-choice group and 104 days in the assay-directed group (hazard ratio 0.8, 95% confidence interval 0.59-1.10, not significant). No difference was seen in overall survival between the groups, although 12/39 (41%) of patients who crossed over from the physician's-choice arm obtained a response. Increased use of combination therapy was seen in the physician's-choice arm during the study as a result of the observed effects of assay-directed therapy in patients. Patients entering the physician's-choice arm of the study during the first year did significantly worse than those who entered in the subsequent years (hazard ratio 0.44, 95% confidence interval 0.2-0.9, P<0.03). This small randomized clinical trial has documented a trend towards improved response and progression-free survival for assay-directed treatment. Chemosensitivity testing might provide useful information in some patients with ovarian cancer, although a larger trial is required to confirm this. The ATP-based tumour chemosensitivity assay remains an investigational method in this condition.

Cell cycle effects of topotecan alone and in combination with irradiation

BACKGROUND AND PURPOSE

To elucidate the role of TP53 on differential effects of topoisomerase I inhibitor topotecan (Hycamtin on radiation sensitivity.

MATERIALS AND METHODS

Cell cycle distribution and protein expression of TP53, p21(WAF1/CIP1) and cyclin B was studied in CCD32 lung fibroblasts, glioblastoma cell lines U118 (mutant TP53), and U87 (wildtype TP53) after treatment with topotecan (0.05 and 1 microM) and/or ionizing radiation (2 Gy).

RESULTS

Cell cycle effects varied with topotecan concentration, resulting in G1 arrest (1 microM), or S/G2/M arrest (0.05 microM), and was modified differentially in fibroblasts and in glioblastoma cells in combination with irradiation. Phosphorylation of TP53 and expression of p21(WAF1/CIP1) was induced by IR and/or topotecan in CCD32 cells, and in U118 cells after topotecan treatment, accompanied by cyclin B degradation. In U87 cells only 1 microM topotecan generated phosphorylation of TP53 and p21(WAF1/CIP1) expression; 0.05 microM caused stabilization of cyclin B.

CONCLUSIONS

The antagonistic effect of combined topotecan/irradiation treatment in fibroblasts was most likely due to an immediate radiation induced G1 arrest, but was not observed in p53 wildtype glioblastoma cells. Thus, the impact of TP53 on the topotecan response remains indistinct, and is obviously influenced by other genomic alterations acquired by tumor cells.

p53 Gene Status and Response to Topotecan-Containing Chemotherapy in Advanced Ovarian Carcinoma

OBJECTIVE

Since the p53 gene has been identified as a determinant of response to chemotherapy in ovarian carcinoma in previous studies, we investigated the significance of the p53 status in response to topotecan as second-line therapy.

METHODS

Twenty-eight patients with advanced ovarian carcinoma, pretreated with standard platinum/paclitaxel chemotherapy, received topotecan as single-agent second-line therapy. Tumors were investigated by molecular analysis for p53 mutations in tumor samples obtained at primary surgery (i.e. before first-line therapy).

RESULTS

Wild-type p53 tumors responsive to first-line therapy maintained substantial responsiveness to topotecan. In contrast, p53 mutation was associated with a low responsiveness to second-line therapy.

CONCLUSIONS

The better outcome in relapsed patients with wild-type p53 suggests that the presence of a functional wild-type p53 confers stability of the drug-sensitive phenotype. This outcome is consistent with the clinical observation that the efficacy of topotecan in the treatment of relapsed ovarian carcinoma patients is dependent on platinum sensitivity, because platinum-sensitive tumors are expected to carry wild-type p53. Although untreated mutant p53 tumors may be responsive to first-line paclitaxel-containing therapy, it is likely that loss of p53 leads to genomic instability resulting in rapid progression to drug resistance.

Thiocolchicine dimers: a novel class of topoisomerase-I inhibitors

During a cellular screening of thiocolchicine analogs, thiocolchicine dimers resulted particularly active in cisplatin-resistant A2780-CIS cells. In order to discover by which mechanism(s) thiocolchicine dimers overcame cisplatin resistance, p53, p21waf1 and MLH1 were assessed by Western blot. Results pointed out that, when combined with cisplatin, dimers increased the amount of all the three proteins with respect to the levels obtained by single drug exposure, thereby suggesting an interference in the process of repair of the cisplatin-induced DNA lesions. Moreover, in isolated nuclei drugs were able to produce DNA breaks, as demonstrated by Comet assay, thereby proving that the compounds were able to target cell nucleus independently from microtubules. Since Topo-I (topoisomerase I) is directly involved in the DNA repair and such activity is overexpressed in cisplatin-resistant cells, Topo-I was investigated as a potential target. Using DNA relaxation assay, thiocolchicine dimers inhibited Topo-I, a property not shared by thiocolchicine. At variance with camptothecin, dimers did not produce cleavable complexes, thereby indicating that Topo-I inhibition occurs upstream of the religation step. To assess the mechanism of inhibition, an electrophoretic mobility shift assay between DNA and Topo-I was performed and revealed that thiocolchicine dimers specifically interfere with binding of Topo-I to DNA. The interference is specific since the same compounds did not modulate DNase activity and did not act as intercalating agents in the DNA unwinding assay. Finally, behaviour of dimers as spindle poisons was investigated and no relevant changes with respect to thiocolchicine in terms of interaction with microtubules were found.

Platinated DNA adducts enhance poisoning of DNA topoisomerase I by camptothecin

Camptothecins constitute a novel class of chemotherapeutics that selectively target DNA topoisomerase I (Top1) by reversibly stabilizing a covalent enzyme-DNA intermediate. This cytotoxic mechanism contrasts with that of platinum drugs, such as cisplatin, which induce inter- and intrastrand DNA adducts. In vitro combination studies using platinum drugs combined with Top1 poisons, such as topotecan, showed a schedule-dependent synergistic activity, with promising results in the clinic. However, whereas the molecular mechanism of these single agents may be relatively well understood, the mode of action of these chemotherapeutic agents in combination necessitates a more complete understanding. Indeed, we recently reported that a functional homologous recombination pathway is required for cisplatin and topotecan synergy yet represses the synergistic toxicity of 1-beta-D-arabinofuranosyl cytidine in combination with topotecan (van Waardenburg, R. C., de Jong, L. A., van Delft, F., van Eijndhoven, M. A., Bohlander, M., Bjornsti, M. A., Brouwer, J., and Schellens, J. H. (2004) Mol. Cancer Ther. 3, 393-402). Here we provide direct evidence for Pt-1,3-d(GTG) poisoning of Top1 in vitro and demonstrate that persistent Pt-DNA adducts correlate with increased covalent Top1-DNA complexes in vivo. This contrasts with a lack of persistent lesions induced by the alkylating agent bis[chloroethyl]nitrosourea, which exhibits only additive activity with topotecan in a range of cell lines. In human IGROV-1 ovarian cancer cells, the synergistic activity of cisplatin with topotecan requires processive DNA polymerization, whereas overexpression of Top1 enhances yeast cell sensitivity to cisplatin. These results indicate that the cytotoxic activity of cisplatin is due, in part, to poisoning of Top1, which is exacerbated in the presence of topotecan.

First-line treatment regimens and the role of consolidation therapy in advanced ovarian cancer

Current first-line management for advanced ovarian cancer consists of cytoreductive surgery followed by chemotherapy, usually with a platinum/taxane combination. Although this approach has been shown to achieve overall response rates of 70-80% in clinical trials, the majority of patients relapse. A number of different approaches have been investigated to improve the efficacy of therapy, including the introduction of newer agents, such as topotecan, into chemotherapy regimens and the use of consolidation therapy. Encouraging results have been obtained in clinical trials of topotecan administered using a variety of different approaches, including replacement regimens, triplet regimens, and sequential doublet regimens. Other treatment modalities have included the use of drug resistance modifiers and intraperitoneal delivery of treatment. A variety of approaches to consolidation therapy have also been investigated, including radiotherapy, cytotoxic therapy, and intraperitoneal therapy. The use of topotecan has also shown promise in this setting, although further data from large, controlled trials are required. In summary, while good response rates are obtained using current first-line treatments, the high relapse rate indicates the need to develop more effective and durable treatment regimens including new agents with, perhaps, an increased emphasis on maintaining remission through the use of consolidation therapy.

Update on the role of topotecan in the treatment of recurrent ovarian cancer

Ovarian cancer is the fifth leading cause of cancer death in women. Most patients with ovarian cancer respond to first-line chemotherapy, but many relapse within 18 to 22 months. The development of efficacious salvage therapies that increase overall survival while maintaining quality of life is a great challenge in the treatment of this disease. Topotecan, a novel topoisomerase I inhibitor, is currently indicated for the treatment of recurrent metastatic carcinoma of the ovary. In patients with relapsed ovarian cancer, the overall response rates on treatment with topotecan range from 19%-33% in platinum-sensitive patients, 14%-18% in platinum-resistant patients, and 5%-11% in platinum-refractory patients. The proportion of patients achieving stable disease ranges between 17% in refractory and 48% in sensitive patients. In phase III studies, topotecan was shown to be equivalent in efficacy to both paclitaxel and liposomal doxorubicin as second-line therapy in patients with relapsed ovarian cancer. Further, non-cross-resistance between topotecan and paclitaxel was demonstrated in a third-line, phase III crossover study, suggesting that topotecan may be effective in the first-line setting with paclitaxel and/or platinum. Hematologic toxicities include neutropenia, thrombocytopenia, and anemia; however, these toxicities are usually short lived, noncumulative, and manageable with dose modifications, including low-dose topotecan regimens. Nonhematologic toxicities are usually mild to moderate in severity. These data support the use of topotecan for second-line therapy and suggest that topotecan may also be effective in first-line therapy. Further studies with topotecan alone and in combination with other agents are needed to fully characterize the role and sequencing of topotecan in the salvage and first-line settings.